Motor vehicles driven by internal combustion engines are well known. Such engines require lubrication to minimize wear of moving parts. In general the lubrication systems in motor vehicles of this type include a crankcase for holding a quantity of oil, an oil line for conducting oil from the crankcase to moving parts to be lubricated under pressure generated by an oil pump and for returning said oil to the crankcase, and a filter through which the oil in said line passes for the purpose of removing contaminants from it.
Under normal operating conditions the lubricating oil of an internal combustion engine tends to become contaminated with an accumulation of foreign material, which, if left in the oil, can be damaging to the engine. Small particles of solid material having dimensions ranging from 10 to 60 microns in diameter are of special concern, since they can do serious damage to the bearing surfaces of the engine. These may be bits of metal, carbon, sand, and other substances. Many patents have been issued on filters and centrifugal devices for use in oil lines of lubricating systems for the intended purpose of purifying the oil by removing contaminants and extending its useful life.
Filters operate on the principle of straining solid contaminants from the oil by some sort of sieve-like marterial through which all of the oil passes. An oil system including a filter has many inherent disadvantages. One disadvantage is that liquid contaminants such as water and acid are not removed. Another is that the pores in the filter material become clogged with contaminants during usage so that the filter ceases to function and has to be replaced periodically, usually when the oil itself has to be changed. Another disadvantage is the difficulty of filtering the oil when it is cold. See, for example, Clare U.S. Pat. No. 2,423,329 granted July 1, 1947.
Centrifugal devices have been proposed for use in lubricating systems which are described as setting up rapid circulatory motion of oil passing through them to cause contaminants to be thrown outwardly through the rotating oil by centrifugal force to form a contaminant-rich phase which is separated from the contaminant-poor phase which is returned to the system. See, for example, Graybill U.S. Pat. Nos. 3,450,264, granted June 17, 1969, 3,529,719 granted Sept. 22, 1970 and 3,888,768 granted June 10, 1975. Careful tests of a device constructed in accordance with the Graybill disclosures established that there was practically no removal of contaminating particles during the time oil was passing through the device. In other words, it is not effective in removing solid contaminants from the oil in a vehicle when the engine is running. While the reason for the failure of this device to operate as predicted in the patents is not definitely known, it is believed to be related to the turbulence and upward currents in the oil during its passage through the doughnut-shaped chamber of the device.